Disconnect of main circuit upon overload in any branch circuit



May 3, 1955 2,707,779

l. GROSS DISCONNECT OF MAIN CIRCUIT UPON OVERLOAD IN ANY BRANCH CIRCUITFiled Oct. 3l, 1952 TO LOAD CIRCUIT FIG. 3 7i-(I. A 2. FROM DCQ3 In K*"0 van@ To LQAP C ,2, l mm CWM' D a O l2. D mwen-wh W im EH@ ISAIIGRE@n fia;

BY I I2' I: 9,24 :M MJ

SUPPLY ATTORNEY United DISCONNECT OF MAIN CRCUIT UPON OVER- LAD IN ANYBRANCH CIRCUIT lsadorc Gross, Philadelphia, Pa., assignor to BurroughsCorporation, Detroit, Mich., a corporation of Michigan This inventionrelates to electronic control systems and particularly to systems inwhich several fuses are employed for different circuits wherein controlrelay means is utilized to protect delicate instruments or tubes inevent of fuse failure in any one of the fused circuits.

Because the load conditions of several electronic circuits connected toa single power supply, and the time delay requirements for protectivedevices connected in the several circuits may be different, it isdesirable to separately fuse different circuits in accordance with themost desirable protection parameters. When the circuits are separatelyfused however, the failure of one fuse may remove bias potentials fromtubes or otherwise cause too much current to flow in other types ofdelicate instruments. Accordingly, an associated control relay circuitis desired to afford proper protection where needed by removing thepotential from those circuits requiring protection or otherwiseactuating protective circuits.

Safety type fuses are available in the art which connect one fuseterminal to an alarm bus when the fuse blows. Therefore these fuses areparticularly adapted for connection to energize a relay from the supplyvoltage source when the fuse fails. Relay contacts may be connected inany desired protective circuit. The control circuit coupled to the alarm'ous must be of the type which is positive acting where delicateinstruments or equipment is utilized, since any failure of actuation ofthe protective circuit caused by sticking of relay contacts or an opencontrol relay winding would destroy the protective quality of the alarmsystem and might cause equipment to be severely damaged.

in the interest of circuit economy it is desirable to provide a singlecontrol relay for all fused circuits. However, when the described alarmtype fuses are connected directly into a plurality of differentpotential leads with a single alarm bus, in the event that two or morefuses would blow simultaneously, the alarm circuit bus would connect thepower supply leads of different circuits toether with possibledisastrous results. Also the different power supply leads are notgenerally of the proper potential for actuating a single control relay.Accordingly, it is desirable to electrically isolate the control circuitcoupled to a single alarm bus from the plurality of power supply leads.

lt is, therefore, a general object of the invention to provide improvedelectronic control systems.

lt is another object of the invention to provide safety alarm fusedcircuits with a positive acting relay protection device.

It is a further object of the invention to provide an alarm circuitactuated by fuse failure in one of a plurality of power supply leads toactuate a single protective control circuit without interconnecting anyof the leads upon the failure of more than one fuse.

In accordance with the teachings of the present invention there is,therefore, provided a fused alarm system utilizing a control relaycircuit wherein the control relay winding is normally coupled to a fusealarm bus and rates Patent fhce 2,797,779 Patented May 3, 1955 a powersupply lead to actuate the relay and is adapted to be short circuitedupon failure of a fuse. The relay therefore is normally energized sothat failure of either a fuse, the relay Winding or relay contactscauses quick and positive actuation of a control or protection circuit.

Other objects and features of advantage of the present invention will befound throughout the following more detailed description of theinvention, particularly when considered in connection with theaccompanying drawing, in which:

Figs. lA and 1B are perspective views of alarm type fuses in an intactand blown condition respectively;

Fig. 2 is a schematic circuit diagram of a control circuit constructedin accordance with one embodiment of the invention; and

Fig. 3 is a schematic circuit diagram of a further control circuitembodying the invention.

Throughout the drawings like reference characters will be used todesignate like circuit elements to facilitate comparison.

Referring in particularity to Fig. l, an alarm type fuse lll is shownhaving two terminals 1l and l2 supported by a dielectric Abody 13 andelectrically coupled by means of a fuse wire l5. A spring assembly i8 issoldered to one end 19 of the fuse wire. A spring plate terminal contact2i electrically connected to terminal 11 is soldered to the other end ofthe fuse wire 22. The spring plate 2i; is adapted to engage an externalfixed alarm terminal or bus 24 when the fuse wire breaks. Accordingly,when an overload occurs and the fuse fails, the spring plate 2 engagesthe alarm bus 24 and provides a short circuit electrical connectionbetween bus 24 and terminal 11 of the fuse.

The circuit of Fig. 2 is adapted to utilize fuses lil or otherprotective devices ot' the type described, where a failure causes amember to contact a unitary alarm bus 2.4 with a power supply terminalstrip l1 upon overload in any one of the separate circuits. Controlrelay winding 29 is connected between terminal strip 1l and alarm bus24. One end of winding 29 is connected to ground through the currentlimiting device 3l so that it is normally energized from the voltagesource 32 at lead 33.

ccordingly, the relay contacts upon deenergization of winding 29 actuateany desirable control or protection circuit so that any circuit failurewill cause a control circuit to assume a position which affordsprotection. As any fuse liti is blown, the control relay winding isshort circuited and accordingly, the relay quickly and positivelyactuates its contacts to return the control circuit into a protectiveposition so that there is little chance for damaging delicate equipmentconnected in the separately fused load circuits when one of thepotential sources is removed.

At times it is desirable to fuse a plurality of diverse leads derivedfrom a direct current power supply. Thus, a bias source, for example,having 25 volts available Vwould be fused differently than a B supplyvoltage having +400 volts available. However, a fuse blowing in the biaspotential supply would not remove the B+ potential f and accordinglyelectronic circuits or tubes might be damaged. An alarm type circuit asshown in Fig. 2 with a single alarm bus, is not in this case desirable,however, since two fuses might simultaneously fail and connect the 25volt supply directly to the +400 volt supplv.

Accordingly, the circuit of Fig. 3 may be utilized to obtainsatisfactory operation where the separate volt age leads are to beseparately fused with devices of the type hereinbefore described. In theillustrated embodiment, the control relay is actuated by an alternatingcurrent supply adapted to provide a single operating potential to therelay winding 29 which is short circuited upon failure of the safetyfuses through a series of relatively low impedance capacitors 35 oisuiicient voltage rating to electrically isolate the alarm bus from thesupply leads to prevent any damage when two or more fuses wouldotherwise interconnect the voltage sources at any two or more of theleads A through F. `he current limiting device di), together with theparticular capacitor 35, which is connected across the control relaywinding 29 when the fuses blow, may serve as a load circuit to preventthe secondary winding of transformer 42; from being short circuited whenthe fuse connects one of the voltage terminals 11 to the alarm bus 24.Therefore it is seen that in accordance with the present invention acontrol relay winding is connected in a normally energized manner sothat the failure of any one of several fuses may cause the relay windingto be short circuited thereby positively actuating a control circuit.

ln the embodiment shown in Fig. 3 the control circuit coupled to thealarm bus 24 is electrically isolated from the power supply leads bymeans of capacitors 3 Accordingly, an improved alarm circuit is providedwhich assures positive operation and the protection of expensive ordelicate electronic circuits even when a plurality of power supply leadsare separately fused.

Having therefore described detailed embodiments of the invention,setting forth its organization and its mode of operation, those featuresbelieved descriptive of the nature of the invention are defined withparticularity in the appended claims.

What is claimed is:

l. An electronic control circuit comprising in combination, a pluralityor direct current leads from a corresponding plurality of power supplyterminals, a plurality of output leads to separate electronic circuits,a plurality of alarm type fuses coupled between said direct currentleads and said output leads, an alarm bus adapted for connection to oneof said direct current leads upon failure of a corresponding fuse, analternating current supply source, a control relay, a circuit includingan impedance device coupling said alternating current supply source tosaid relay by way of said alarm bus and a further lead, and a pluralityof capacitors coupling each of said direct current leads to said furtherlead, whereby failure of more than one fuse will short circuit saidcontrol relay without interconnecting any of the power supply terminals.

2. A control system comprising, in combination, a circuit connectible toa source of electrical energy, a plurality of direct current voltageterminals connected into said circuit, a plurality of load circuit leadsconnected to said terminals, an alarm bus connected to the circuit, aplurality ot' alarm type fuses, one for each of said leads, each of saidfuses normally being out of engagement with the alarm bus but operableupon fuse failure to connect its lead to the alarm bus, and analternating current control relay including an energizable winding andan armature controlled switch, the winding of the relay beingelectrically connected to the alarm bus and capacitively coupled to eachof said leads, a further lead electrically connected to said circuit anddirectly to the capacitively coupled side of said winding, the switch ofthe relay being operable to open and close the connection of saidcircuit to its source of electrica] energy.

3. A control system comprising, in combination, a circuit connectible toa source of electrical energy, a plurality of Voltage terminalsconnected in to said circuit, a plurality of load circuit leadsconnected to said terminals, an alarm bus, a plurality of alarm typefuses, one for each of said leads, each of said fuses normally being outof engagement with the alarm bus but operable upon fuse failure toconnect its lead to the alarm bus, and a control relay including anenergizable Winding and an armature controlled switch, the winding ofthe relay be ing electrically connected between said alarm bus and saidcircuit, the switch of the relay being operable to open and close theconnection of said circuit to its source of electrical energy.

4. A control system comprising a power supply circuit connectible to asource of electrical energy, a plurality of load circuit leads eachconnected to said power supply circuit, an alarfn bus connected to thepower supply circuit, an alarm type fuse in each of said load circuitleads, each fuse normally being out of engagement with the alarm bus butoperable upon overload and corresponding use failure to connect the leadwith which it is associated to the alarm bus, a control relay includingan energizable winding and an armature actuated switch, said relaywinding eing electrically connected between the alarm bus and the powersupply and normally energized as a result thereof, said relay switchnormally act- `ing to close said power supply circuit when the relaywinding is thus eneroized but actuable to open the circuit when thewinding is Cie-energized by the shorting of any one of the circuit leadswith the alarm bus caused by the engagement of any one of said alarmtype fuses with the alarm bus.

References Cited in the le of this patent

